1. Field of the Invention
The present invention generally relates to fuses within integrated circuit devices and more particularly to an imbalanced sense amplifier circuit that detects high resistance programmed fuses.
2. Description of the Related Art
Fuses are used in semiconductor manufacturing processes for a number of reasons and are primarily utilized to protect or selectively connect/disconnect devices within the integrated circuit. Fuses can be used to change the logic of the integrated circuit by making or breaking connections between logic devices. Similarly, fuses can be utilized to disconnect defective devices from the remaining properly operating devices. As is well known to those ordinarily skilled in the art, fuses within semiconductor devices have a number of other functions.
There are two broad types of fuses, the first being a fuse and the second being an antifuse. A traditional fuse forms an electrical connection until it is opened (e.g., programmed, blown, etc.). To the contrary, an antifuse naturally resides in a disconnected state and only forms an electrical connection when it is closed (e.g., programmed, blown, etc.).
When an antifuse is blown, an insulator between two conductors is destroyed and the conductive portions within the fuse join to form an electrical connection. However, sometimes the electrical connection that is made still retains a large portion of the insulator material and has a high resistance. The intent in programming the antifuse is to form a low resistance electrical connection; however, if the blown antifuse has a high resistance, the integrated circuit may operate as if the antifuse had never been closed. Similarly, conventional poly electrical-fuses have a very low resistance (poly efuses) before programming. When the poly efuse is programmed (blown), the xe2x80x98openxe2x80x99 fuse resistance can be marginal (e.g., remain low), which presents a problem similar to a blown antifuse. The invention discussed below solves these problems using a novel circuit design.
It is, therefore, an object of the present invention to provide a circuit adapted to sense the status of a fuse. An imbalanced sense amplifier latch which includes first and second portions connected to the fuse. The first portion of the latch is connected to a fuse and is weaker than the second portion, allowing the first portion to sense a lower voltage. The voltage difference between the portions indicates the conductive status of the fuse.
The first portion includes devices having a gate size smaller than that of the devices in the second portion. The invention also includes a first transistor between the fuse and the imbalanced sense amplifier latch and a second transistor between the imbalanced sense amplifier and ground. The delay between activation of the transistors controls a sensing resistance threshold of the circuit. Several precharge devices are connected to the imbalanced sense amplifier latch. More current flows through the first than the second in an antifuse application.